Kids mattress sizes

Children move through several mattress sizes. The first is regulated: in the United States, a full-size crib mattress must measure at least 27 1/4 inches wide and 51 5/8 inches long under the federal safety standard for crib mattresses cited below, which incorporates the ASTM crib mattress specification. The crib itself is regulated separately: a full-size crib has an interior of 28 inches wide and 52 3/8 inches long, each within 5/8 of an inch. The mattress minimums and the crib interior are set together so that the gap between mattress and crib side stays small.

Crib and toddler bed

In metric terms the crib mattress minimum is 690 by 1,310 millimetres, about 69 by 131 cm, and the full-size crib interior is about 71 by 133 cm. The standard also limits how far the mattress can be pushed into a corner and still leave a gap, which is why a crib mattress should be bought to the full-size specification rather than approximated. Many toddler beds are built around the same full-size crib mattress, but that is a product design choice; check the toddler bed's labelling for the mattress it is designed to hold. Non-full-size cribs, bassinets and play yards use mattresses matched to the specific product, and the federal standard requires those after-market mattresses to be tested with the product they are sold for.

The move to a Twin

When a child outgrows a toddler bed, the usual next size in the US profile is a Twin at 38 by 75 inches, about 96.5 by 190.5 cm. A Twin is also the standard size for bunk beds and most children's bed frames. A Twin XL at 38 by 80 inches adds 5 inches of length and is worth considering for a tall teenager, because the width is the same and only the frame length changes.

Full for older children and shared rooms

A Full at 54 by 75 inches gives a growing child or teenager 16 inches more width than a Twin at the same length. In a shared room, two Twins take more floor space than one Full but give each child a separate bed; the room calculator on this site checks either arrangement with your measurements. These three sizes use the same nominal profile as the rest of this site.

What this page does not cover

Firmness, materials and chemical safety are outside the scope of this site. The regulations cited here set dimensions and fit; they are quoted for the United States only, and other countries use different crib and cot standards.